As an impact tool for fastening a screw, a bolt or the like, there is known an oil pulse tool that generates a strike force by utilizing a hydraulic pressure. An oil pulse tool typically has a low operating sound since there is not an impact between metals. According to such an oil pulse tool, a motor is used to drive an oil pulse unit, and an output shaft of the motor is directly connected to the oil pulse unit. When a trigger switch for operating the oil pulse tool is pulled, the motor is driven.
In such an oil pulse tool, oil inside of the oil pulse unit may leak over a long period of use. In such a case, the oil pulse unit may need to be replaced to prevent spreading of the leaked oil inside of a housing of the tool. By continuing to use the tool without noticing the oil leakage, the motor, a control circuit or the like may be damaged, and, as a result, the entire tool may need to be replaced. Hence, according to the below referenced patent (PTL 1), in a pneumatic type oil pulse tool, a fastening energy amount generated by one strike is calculated. A sensor is used to measure a hydraulic pressure pulse generated by an oil pulse unit. The fastening energy is calculated by integrating the pressure pulse over time. When the calculated fastening energy amount generated by one strike becomes equal to or lower than a set value, a determination is made that the fastening capability of the impulse wrench has deteriorated, and a deterioration alarm is issued.